4.5 Cell-mediated immune response

cell-mediated immunity

Driven by T cells, defends against intracellular pathogens by directly attacking infected cells. 

Thymocytes

immature T cells that develop into fully functional T cells through positive and negative selection.

T cell tolerance

The process of eliminating T cells that might attack the cells of one’s own body

epithelial cells

While T cells are developing in the cortex of the thymus, they are first exposed to

positive selection

if thymocytes bind to the MHC molecules on the epithelia in the thymus, the MHC molecules of “self” are positively selected.

negative selection

self-antigens are presented to the immature T cells by peptide-presenting cells of the thymus. If they attach, then they are destroyed through apoptosis.

class I or class II

Inactive T cells have receptors that bind to____MHC proteins

CD markers

markers found in T cell membranes. The molecular basis of antigen recognition

CD8

Markers respond to antigens on class I MHC proteins and are found on cytotoxic T cells, regulatory T cells, and memory T cells.

CD4

Markers respond to antigens on class II MHC proteins and are found on helper T cells and memory TH cells.

the CD4 marker or the CD8 marker

Mature T cells express either______

Self major histocompatibility proteins

T cells must recognize_____ during positive selection

Self-antigens

T-cells must not recognize______ during negative selection.

clonal expansion

Proliferation of T cells is called_____

clone 

a group of lymphocytes that share the same antigen receptor

antigen

Only those clones of lymphocytes whose receptors are activated by the____ are stimulated to proliferate.

polyclonal response

the stimulation of multiple types of T cell clones.

costimulated

T cell to be activated, it must also be_____

Cytotoxic T cells (Tc)

T cells that kill target cells by inducing apoptosis using a similar mechanism as NK cells to release

Perforins

insert into the target cell membrane, forming pores like those produced in complement activation.

Cytokines

chemical messengers that activate genes in the target cell to trigger apoptosis.

Granzymes

enter the cell via the pores and degrade the cellular contents.

Regulatory T cells

suppressor T cells, also form from CD8 T cells. These cells act to suppress other T cell immune responses and suppress antibody activation.

Helper T cells

bearing the CD4 molecule, respond to antigens presented on class II MHC.

Th1 helper cells

a type of effector helper T cell that secrete cytokines to activate cytotoxic T cells.

Th2 helper cells

a type of effector helper T cells that secrete cytokines to cause B cells to differentiate into antibody-producing plasma cells.

Memory helper T cells (TH)

are also created to continue immune surveillance and can activate if a pathogen is detected later.

memory T cells and effector T cells

During a primary adaptive immune response, both ______ are generated.

organ transplantation

Involve replacing failing organs with healthy ones from donors, typically those who are recently deceased and had volunteered or whose families donated their organs.

transplant rejection

Occurs when the recipient's immune system identifies the transplanted tissue or organ as foreign, triggering an immune response that attacks and ultimately destroys the graft.

Histocompatibility

The property of having the same, or mostly the same, portion of genes that code for the major histocompatibility complex (MHC) molecules

MHC polygeny

the multiple MHC proteins on each cell

MHC polymorphism

Multiple alleles for each person’s MHC molecules

graft-versus-host disease

Since the recipient’s immune response has been destroyed before receiving the transplant, the donor cells may attack the recipient’s other tissues

Immunosuppressive drugs

have made transplants more successful. These drugs act by diminishing the strength of the body's immune response to prevent it from attacking a transplanted organ or tissue.